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POWhat is the quickest way to compare a C# Dictionary to a 'gold standard' Dictionary for equality?
 

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  1. POWhat is the quickest way to compare a C# Dictionary to a 'gold standard' Dictionary for equality?
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    <p>I have a known-good Dictionary, and at run time I need to create a new Dictionary and run a check to see if it has the same key-value pairs as the known-good Dictionary (potentially inserted in different orders), and take one path if it does and another if it doesn't. I don't necessarily need to serialize the entire known-good Dictionary (I could use a hash, for example), but I need some on-disk data that has enough information about the known-good Dictionary to allow for comparison, if not for recreation. What is the quickest way to do this? I can use a SortedDictionary, but the amount of time required to initialize and add values counts in the speed of this task.</p> <p>Concrete example:</p> <p>Consider a Dictionary<code>&lt;String,List&lt;String&gt;&gt;</code> that looks something like this (in no particular order, obviously): </p> <pre><code>{ {"key1", {"value1", "value2"} }, {"key2", {"value3", "value4"} } } </code></pre> <p>I create that Dictionary once and save some form of information about it on disk (a full serialization, a hash, whatever). Then, at runtime, I do the following:</p> <pre><code>Dictionary&lt;String,List&lt;String&gt;&gt; d1 = new Dictionary&lt;String,List&lt;String&gt;&gt; (); Dictionary&lt;String,List&lt;String&gt;&gt; d2 = new Dictionary&lt;String,List&lt;String&gt;&gt; (); Dictionary&lt;String,List&lt;String&gt;&gt; d3 = new Dictionary&lt;String,List&lt;String&gt;&gt; (); String key11 = "key1"; String key12 = "key1"; String key13 = "key1"; String key21 = "key2"; String key22 = "key2"; String key23 = "key2"; List&lt;String&gt; value11 = new List&lt;String&gt; {"value1", "value2"}; List&lt;String&gt; value12 = new List&lt;String&gt; {"value1", "value2"}; List&lt;String&gt; value13 = new List&lt;String&gt; {"value1", "value2"}; List&lt;String&gt; value21 = new List&lt;String&gt; {"value3", "value4"}; List&lt;String&gt; value22 = new List&lt;String&gt; {"value3", "value4"}; List&lt;String&gt; value23 = new List&lt;String&gt; {"value3", "value5"}; dict1.add(key11, value11); dict1.add(key21, value21); dict2.add(key22, value22); dict2.add(key12, value12); dict3.add(key13, value13); dict3.add(key23, value23); dict1.compare(fileName); //Should return true dict2.compare(fileName); //Should return true dict3.compare(fileName); //Should return false </code></pre> <p>Again, if the overall time from startup to the return from compare() is quicker, I can change this code to use a SortedDictionary (or anything else) instead, but I can't guarantee ordering and I need some consistent comparison. compare() could load a serialization and iterate through the dictionaries, it could serialize the in-memory dictionary and compare the serialization to the file name, or it could do any number of other things.</p>
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    1. USShea Levy
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      1. POWhat is the quickest way to compare a C# Dictionary to a 'gold standard' Dictionary for equality?
      1. USCos Callis
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    1. COPlease confirm that you are seeking "value equality" as a comparison? The way the question is worded I believe this is the case, but I want to be certain.
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      1. POWhat is the quickest way to compare a C# Dictionary to a 'gold standard' Dictionary for equality?
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    2. COWhen optimizing tasks like this it is helpful to be clear about what case you're optimizing for. Is the common case that needs to be optimized that the two dictionaries are the same, or that they are different? The reason I ask is because a common optimization technique is to do a cheap test that catches 99% of the "different" cases, and then an expensive test that confirms identity. Obviously that is not a good optimization if most of the time the dictionaries really are identical; the cheap test just slows you down.
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      1. USEric Lippert
    3. COCos Callis: If, for each String-List<String> pair in the known-good dictionary, there is a String-List<String> pair in the dictionary to be checked that has the same valued String as the key and a List with the same valued Strings in the same order as the value, then I want true, otherwise false.
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      1. USShea Levy
 

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